1. Technical Field
The present invention relates to a tuning fork oscillating piece, a tuning fork oscillator, and an acceleration sensor, which include drive piezoelectric thin film element and detection piezoelectric thin film element.
2. Related Art
Currently, a thin film miniaturized mechanical type resonator (hereinafter referred to as piezoelectric thin film tuning fork oscillating piece) which includes a base, two arms extending from the base (hereinafter referred to as oscillating arms), drive units (hereinafter referred to as drive piezoelectric thin film elements) and detection units (hereinafter referred to as detection piezoelectric thin film elements) provided on the main surfaces of each of two oscillating arms has been disclosed (for example, see JP-A-2003-227719, pp. 11-16, FIGS. 8-13). This type of piezoelectric thin film tuning fork oscillating piece is included in a gyro element and the like. Each of the drive piezoelectric thin film elements has first and second electrodes (hereinafter referred to as drive lower electrode sections), first and second piezoelectric thin films disposed on the first and second drive lower electrode sections (hereinafter referred to as drive piezoelectric thin film sections), third and fourth electrodes disposed on the first and second drive piezoelectric thin film sections (hereinafter referred to as drive upper electrode sections), provided on the inner and outer sides of a center line on the main surface of the oscillating arm units in an extension direction of each oscillating arm unit (hereinafter referred to as main surface center line) such that a clearance is produced between the first and second drive lower electrode sections. Each of the detection piezoelectric thin film elements has fifth electrode disposed away from the first and second drive lower electrode sections (hereinafter referred to as detection lower electrode section), a third piezoelectric thin film disposed on the detection lower electrode section (hereinafter referred to as detection piezoelectric thin film section), and a sixth electrode disposed on the detection piezoelectric thin film section (hereinafter referred to as detection upper electrode section). The drive piezoelectric thin film sections and detection piezoelectric thin film sections are both chiefly made of titanic acid zirconic acid lead (hereinafter referred to as PZT). The inner side herein refers to the side extending toward the center line between the two oscillating arms (between the main surface center lines) from the main surface center lines, and the outer side herein refers to the side extending away from the respective main surface center lines.
According to the piezoelectric thin film turning fork oscillating piece in this related art, the drive piezoelectric thin film sections and the detection piezoelectric thin film sections are both chiefly made of PZT. The absolute value of the piezoelectric d constant, which is the piezoelectric strain constant, of the PZT (hereinafter referred to as “d”) is a relatively large value in the absolute values of d of other piezoelectric materials. Thus, PZT has an advantage of converting predetermined electric energy into mechanical energy with high efficiency. However, the absolute value of the piezoelectric g constant, which is the piezoelectric output constant, of PZT (hereinafter referred to as “g”) is relatively small in the absolute values of g of other piezoelectric materials. Thus, PZT cannot convert predetermined mechanical energy into electric energy with high efficiency.
Accordingly, the related-art piezoelectric thin film turning fork oscillating piece cannot achieve improvement in both driving efficiency and detection sensitivity.